1. Field of the Invention
The invention relates generally to fluid mixing devices. More specifically, the invention relates to means to cause rotational flow of fluid. In still greater particularity, but without limitation thereto, the invention relates to a device that causes axial vortices and azimuthal instabilities in a first fluid to enhance mixing of the first fluid with a second fluid.
2. Description of the Prior Art
The efficient mixing of fluids is crucial for the operation of many devices. Among these devices, for example, are chemical reactors, combustors and lasers.
Large scale mixing or bulk mixing of fluids has been achieved by contacting a jet of one fluid with a second fluid. The flow instabilities existing at the boundary layer of the jet causes an entrainment of the second fluid within the first fluid.
To achieve efficient mixing however, especially when a reaction is involved, consideration must be given not only to large scale mixing, i.e. the integrated amount of mixed components, but also to small scale mixing, i.e. the amount of molecular mixing.
Much research has been done to develop methods for augmenting both large and small scale mixing. Active methods, those utilizing energy from an external source, and passive methods, those utilizing the internal energy of the fluid or fluids being mixed, have been employed depending upon the enviroment in which the mixing is to take place.
A passive method that has been studied uses a small aspect ratio elliptic nozzle. Entrainment into a jet emitted from this elliptic nozzle, compared to a jet emitted from a circular nozzle, was substantial. Large scale mixing was considerably increased, relative to the circular nozzle, due to an induction effect of elliptical vortices created by this nozzle. Small scale mixing was also enhanced, due to high azimuthal instability modes that are amplified by this non-circularly shaped nozzle.
Although the elliptical nozzle does contribute to improved mixing, a variety of applications could benefit from even greater mixing, particularly, small scale mixing. Further, for the elliptic nozzle, the increase in the level of turbulence in the core of the jet is relatively slow in the downstream direction. This is considered a drawback when a high mixing rate is required throughout the flow field. Additionally, there are situations in which mixing space is quite limited, compelling the need for a mixing device that provides efficient mixing in a relatively small space. While the elliptic nozzle has exhibited superior characteristics in this respect, a device that efficiently mixes fluids in an even smaller space would be worthy.